In the cryogenic rectification of feed air into nitrogen and oxygen products, the oxygen is typically produced at a purity of about 99.5 mole percent. Because of the relative volatilities of the components of air, the argon in the feed air tends to concentrate with the oxygen rather than with the nitrogen. Accordingly, the remainder of the typical oxygen product stream from a conventional cryogenic air separation process is comprised primarily of argon.
For most uses, the presence of this small amount of argon in the oxygen stream is not a problem. However, in some situations, such as in the use of oxygen in the production of chemicals such as ethylene oxide, the argon, owing to its inertness, undergoes a buildup within the chemical reactor requiring a periodic venting of the reactor so as to avoid retarding the production reaction. This periodic venting causes a loss of valuable products.
The problem of production reaction burden due to argon buildup can be addressed by increasing the purity of the oxygen input to the reactor, and systems for producing oxygen of higher than conventional purity are known. However, such systems generally can produce only relatively small quantities of elevated purity oxygen. Moreover, such systems are generally not readily adaptable to existing cryogenic rectification systems designed to produce oxygen of conventional purity.
Accordingly, it is an object of this invention to provide an improved cryogenic rectification system for the production of very high purity oxygen.
It is another object of this invention to provide an improved cryogenic rectification system for the production of very high purity oxygen which can be easily retrofitted to existing systems designed to produce oxygen of conventional purity.